Metal salts of phosphorodithioic acids are known lubricant additives. See, for example, U.S. Pat. Nos. 3,390,082 and 4,326,972. Metal salts of mixtures of phosphorodithioic acids and carboxylic acids are also known lubricant additives. See, for example, U.S. Pat. No. 4,308,154.
Preparations of phosphorodithioic acid usually involve the reaction of phosphorus pentasulfide (P.sub.2 S.sub.5) and an alcohol or a phenol. A problem that arises with these preparations is that they often result in levels of active sulfur that are unacceptable for certain applications due to the corrosive nature of active sulfur. For example, certain hydraulic fluids containing an excess of about 300 ppm active sulfur (as measured by IP-155) may under various circumstances stain or corrode copper and similar materials.
The sulfurization of olefinically unsaturated compounds at relatively low temperatures of about 140.degree. C., for example, requires relatively long reaction times and the products of such sulfurizations tend to have levels of active sulfur that are unacceptable for various applications such as lubricants or functional fluids intended for use with copper or similar metals. When the sulfurization is conducted at higher temperatures of about 150.degree.-180.degree. C., for example, very dark to black products are often obtained which when employed in lubricants or functional fluids usually result in dark oil solutions that are commercially unacceptable.
It would be advantageous to provide metal salts of phosphorus-containing acids, or metal salts of mixtures of such phosphorus-containing acids and carboxylic acids that have sufficiently low levels of active sulfur so that such salts or lubricants or functional fluids containing such salts would not stain or corrode copper or similar materials. It would also be advantageous to sulfurize olefinically unsaturated compounds at relatively low reaction temperatures (i.e., below about 140.degree. C.) and relatively short reaction times, and provide compositions that are relatively light in color and have sufficiently low levels of active sulfur so that such compositions or lubricants or functional fluids containing such compositions would not stain or corrode copper or similar materials.
U.S. Pat. No. 4,289,635 discloses molybdenum-containing compositions prepared by reacting an olefinically unsaturated compound capable of reacting with active sulfur with a composition prepared by reacting (a) a phosphorus containing acid represented by the formula ##STR2## wherein each X and X' is independently oxygen or sulfur, each n is 0 or 1 and each R is independently the same or different hydrocarbon-based radical, and (b) at least one hexavalent molybdenum oxide compound, and (c) hydrogen sulfide, in the presence of (d) a polar solvent. These compositions are described as being useful as additives for lubricants.